Tube-bending mandrel



y 1948- R. F. ATTRIDGE 2,444,907

TUBE-BENDING MANDREL Filed May 5, 1945 I U-\ FIG. I. a 6

INVENTOR RICHARD F. ATTRIDGE QM W ATTORNEY Patented July l3, 1948 OFFICE TUBE-BENDING MANDREL Richard F. Attrldge, Revere, Mass. Application May 3, 1945', Serlal No. 591,769

( Granted under the act of March a, 1883, as amended April 30, 1928; 370 0. G. 757) 3 Claims.

My invention relates to a tube-bending mandrel. It has to do more particularly, with a mandrel adapted to be disposed within a tube and having a flexibly mounted bearing unit located where the tube is to be bent in order tomaintain the cross-sectional shape of the tube during bending.

In bending thin-wall metal tubes at present, especially with short-radius bends. it is customary to pack the tube with sand or fill it ,with molten resin which is allowed to solidify in order to prevent collapse of the tube at the area of bending. In bending the tube, the tendency for the outer side of the tube to collapse is caused by the extreme tension developed in the material of the outer side during the bending operation. On the other or inner side there is a tendency for the material to ripple or wrinkle due to the extreme compression developed in the'material of the inner side during the bending operation. The sand or resin used in an attempt to prevent collapse or wrinkling is removed after bending the tube. bviously, this method is slow and cumbersome.

A mandrel has been designed and used in an attempt to maintain the cross-sectional shape of the tube at the bend. This mandrel includes a rod having a ball swiveled on its end. The ball is adaptedto be disposed within the tube where it is bent to prevent collapse thereof. I have found that the ball does not keep the tube from flattening on the outer side of the bend, especially when the tube is being bent to-a short radius. This is bending mandrel which has abearing unit illustrated in the accompanying drawing wherein due to the fact that the ball does not afiord a bearing surface of sufllcient extent lengthwise of the bend. Consequently, the flattening 0f the tube on the outer side of the bend usually occurs beyond the ball. Furthermore, the single ball does not prevent the metal of the tube from rippling on the inner side of the bend, especially with short radius bends.

One of the objects of my invention is to provide a tube-bending mandrel having means associated therewith for eilectively maintaining the crosssectional shape of the tube at the bend.

Another object of my inventionis to provide a mandrel oi the type indicated having a bearing unit oi such a nature that it will afford sufllcient swiveled on the end thereof: This bearing unit consists of a single member having a convex hearing surface at each end and an intermediate concave ironing surface.

The preferred'embodiment of my invention is similar characters of reference designate corresponding parts and wherein:

Fig. l is a plan view, partly broken away, illustrating'my tube-bending mandrel in position in a tube being bent.

" Fig. 2 is a longitudinal sectional view illustrat-' ing in detail the bearing unit of my mandrel.

Fig. 3 is a longitudinal sectional view through the tube showing my mandrel in position in the tube before it is bent.

Fig. 4 is a similar view but showing the tube after it is bent. Fig. 5 is an end view of the bearing member of my mandrel.

With reference to the drawing, 1 have illustrated in Fig. l, clamping-units l and 2 of a tubebending machine. These units l and 2 are of the usual type, the unit I being mounted in a fixed 1 position and the unit 2 being mounted for swinging movement about a pivot point 3. This pivot point 3 is the center about which the tube 4 is to bebent. Initially, the clamping-unit 2 is disposed directly adjacent to the unit I, as indicated by the dotted lines, so that these units are in side-by-side relationship. When the tube 4 is being bent, the unit 2 is swung about the point 3 and may, if desired, be swung through an angle of 180 to the full line position indicated in Fig; 1. The unit I and the unit 2 areprovided with the usual tubeembracing dies which are opened and closed by bearing surface to prevent flattening of the tube handwheels 5 and 6, respectively.

A mandrel I is inserted in the tube 4 before it is bent. The mandrel is secured in a fixed position within tube 4, prior to bending the tube, by suitable means (not shown) attached to the bending machine and carries the bearing unit of my invention. Thus, the mandrel I includes a rod having its inner end 8 threaded into a bushing 9 which. in turn, is threaded into the end of a sleeve ID. This sleeve III is of the same diameter as the internal diameter of the tube 4 to be bent. The hollow chamber ll within the sleeve communicates at its forward end with a reduced bore l2 in which is formed a ball seat i3. This ball seat i3 is adapted to receive a spherical or ball-like portion l4 formed on the inner end of a screw bolt IS. The bolt 15 is positioned by inserting it through the chamber I I, before positioning sleeve III on the mandrel rod, and passing it outwardly through the bore l2. The outer end of bore I2 is flared. as indicated at It. to permit swinging of the bolt 15 in all directions relative to the sleeve It. The forward end of the sleeve I is machined to form an annular recess 11 and thereby produce a peripheral flange l8.

The outer or forward end of the bolt II is threaded,' as indicated at l3, and receives a threaded ball portion 20. The ball portion 20 is secured in the desired adjusted position on the bolt I by a lug 2| which is attached to the flat forward face of the ball portion. This lug 2i has a flat edge for cooperating with either of the flattened sides 22 (Fig. 5) of the outer end of bolt l5, to prevent rotation of ball portion 23 on the bolt.

The bolt l5 and ball portion 20 serve to connect the sleeve i ll flexibly to a bearing member 23. This bearing member is in the form of a sleeve having a bore 23a extending therethrough. The bore 23a has a ball seat 25 formed therein adiacent to its inner end for cooperating with the ball portion 28. The inner end of the bore, through which bolt it passes is flared, as indicated at 26, to permit free swinging of member 23 relative to bolt I! in all directions. The recess H in the outer end of sleeve ill will also facilitate this'swinging action, preventing interference between the adjacent ends of members Ill and 23. As shown best in Figs. 3 and 4, the bearing member 23 has convex bearing surfaces 21 and 28 formed on its outer surface adjacent to the ends thereof. Between these bearing surfaces is a concave ironing surface 29 which merges with both the surfaces 21 and 28. All of the surfaces 21, 28, and 23 extend completely around the member 23 which is of annular form. The diameter of the greatest transverse section of member 23, taken through either of the convex portions 21 or 23, will correspond substantially to the internal diameter of the tube 4 to be bent. In bending the tube, the unit 2 is positioned in the dotted-line posltlonindicated in Fig. l and the mandrel 1-is anchored in position on the machine. The mandrel will carry one of my bearing members 23 which will have convex portions 21 and 23 that have maximum outside diameters corresponding substantially to that of the internal curvature of the tube 4 to be bent. The sleeve Ill, carried by the mandrel, also has an outside diameter corresponding to the internal diameter of the tube 4. The tube 4 will be in the straight-line position indicated by the dotted lines in Fig. 1. The mandrel will be so positioned that the outer or forward end of sleeve It will be substantially in alignment with the center of pivot 3.

The machine is now operatedto swing the unit 2 around the pivot 3. In the example shown, the unit 2 is swung through 180 but it is to be understood that it may be swung through any selected angle to bend the tube to any desired extent. During the bending of the tube, the bolt I5 is free to rock relative to sleeve l3, due to. the ball and socket connection 13-. Also the member 23 will be free to rock relative to the bolt '15, due to the ball and socket connection 20-25. Thus, the member 23 will readily rock and move with the tube as it is being bent and member 23 rocks, its inner and adjacent the inner side of the bend of the tube will swing into the recess I1, as indicated in Fig. 2.

of the tube bears against the convex surfaces 21 and 23. These convex surfaces 21 and 23 are spaced apart longitudinally a, considerable distance so that bearing surfaces will be provided at widely spaced longitudinal intervals. Furthermore, the surface 23 will be a considerable distance from the forward end of sleeve l0. Thus,

flattening of the outer side of the bend of the the internal surface of the tube will shift longitudinally of member 23. The'original line of contact between each of these convex surfaces and the tube is indicated by the broken line A in Figs. 3 and 4. As the tube is bent, the lines of contact shift through successive positions to the positions indicated by the full line B. Due to the fact that the member 23 is free to rotate on its axis, the contact between the surfaces 21 and 23 and the surface of the tube may occur on either side of line A, depending upon whether the contact is with the outer side or inner side of the bend, through a distance equal to the distance between lines A and B. Since the contact may be at any point between lines A and B and at any point between line A and the same distance on the opposite side thereof, that is, to the line C, it is important that the radius of curvature, longitudinally of member 23, of the surface extending from B to C be the same as that of the outer side of the bend of the tube. Thus, the radius of curvature. of the surfaces 21.

- and 2B, longitudinally of member 23, will correspond to that of the outer side of the bend of the tube. The center of the curvature of such surfaces, longitudinally of member 23, will be at the center of pivot 3, about which the tube is to be bent. The center of curvature of such surfaces, transversely of member 23, will be at the center of the tube. Thus. the convex surfaces 21 and 28 are toric surfaces.

The concave surface 28 is also a toric surface and will have a radius of curvature, longitudinally of member 23, corresponding to that of the inner side of the bend of the tube, with its center at the center of the point 3, as indicated in Fig. 4. The center of the curvature of such surface, transversely of member 23, will be at the center of the tube.

As the tube bends. the material thereof tends to ripple or wrinkle along the inner side of the bend, where it contacts with member 23. due to the compression of the material. However, the

wheels 5 and 3 areactuated to operate the dies 2 to release the tube. Then it is merely necessary to grasp the curved portion of the tube and pull the tube out of the dies and off the mandrel.

It will be apparent from the above description that I have provided a bearing unit on a tubebending mandrel having a number of advantages. it is also free to rotate about its axis. As the The bearing unit will provide suflicient surface, properly located, to prevent flattening of the tube on the outer side of the bend. The bearing unit will iron out the throat of the tube and prevent As the tube is bent, the outer side of the head wrinkling thereof. This will eliminate danger of the die portion 24 cutting into the throat. Furthermore, it will prevent chattering or vibration,

invention, what I member attached to the end of the mandrel by a universal connection and adapted to be located within said tube where it is to be bent, said bearing member having a plurality of convex bearing portions formed thereon at longitudinally spaced intervals and a concave ironing portion disposed therebetween, the surfaces of said bearing portions being curved longitudinally of said bearing member the same as the curvature of the outer side of the bend to be formed in the tube and said concave ironing surface being curved longitudinally with .the same radius of curvature as that of the inner side of the bend to be formed in the tube, the surface of said ironing portion merging with the surfaces of said bearing portions, said bearing member being of annular cross section so that it will fit closely within the tube to be bent.

2. In a mandrel for bending a tube, a bearing member attached to the end of the mandrel and adapted to be located within said tube where it is to be bent, said bearing member having a Plurality of convex bearing portions formed thereon at longitudinally spaced intervals and a concave ironing portion disposed therebetween, the surfaces of said bearing portions being curved longitudinally of said bearing member the same as the curvature of the outer side of the bend to be formed in the tube.

3. In a mandrel for bending a tube, a bearing member attached to the end of the mandrel and adapted to be located within said'tube where it is to be bent, said bearing member having a plurality of convex bearing portions formed thereon at longitudinally spaced intervals and a concave ironing portion disposed therebetween, said concave ironing portion merging with the surfaces of said bearing portions and being curved longitudinally with the same radius of curvature as that of the inner side of the bend to be formed in the tube. 9

RICHARD F. AT'I'RIDGE.

REFERENCES orrEn The following references are of record in the file of this patent: 

